Ring Enlargements of in Situ-Formed Cyclopropanones by Sulfoxonium Ylides: One-Pot Synthesis of Alkylidene Cyclobutanones

A one-pot method for the stereoselective synthesis of alkylidenecyclobutanones from cyclopropanone surrogates is reported. Reaction partners are stable sulfoxonium ylides, leading to the four-membered rings in up to 84% yield. Mechanistic studies indicate that the transformation proceeds via nucleophilic attack of the sulfoxonium ylide on the three-membered ring, followed by ring enlargement. The stereochemical outcome of the ring expansion is substituent-dependent: alkyl groups promote complete retention of configuration, whereas aryl groups result in partial erosion of enantiopurity.